Electroporation is a widely-used method for permeabilization of cell membranes by temporary generation of membrane pores with electrical stimulation. The applications of electroporation include the delivery of DNA, RNA, siRNA, peptides, proteins, antibodies, drugs or other substances to a variety of cells such as mammalian cells, plant cells, yeasts, other eukaryotic cells, bacteria, other microorganisms, and cells from human patients. Electrical stimulation may also be used for cell fusion in the production of hybridomas or other fused cells. Electrical cell fusion may be regarded as a special form of electroporation.
During a typical electroporation, cells are suspended in a buffer or medium that is favorable for cell survival. For bacterial cells electroporation, low conductance medium, such as water, is often used to reduce the heat production by transient high current. The cell suspension is then placed in a rectangular cuvette embedded with two flat electrodes for an electrical discharge. For example, Bio-Rad (Hercules, Calif.) makes Gene Pulser line of products to electroporate cells in cuvettes. Traditionally, electroporation requires high field strength.
The electroporation process is usually toxic to the cells. First, when the electric field strength is too high, the cell membranes may be irreversibly damaged. Secondly, while electrically induced membrane pores allow a target substance to enter the cells, the pores may also allow outflow of cellular contents and inflow of other unintended substances which could negatively affect cell viability. Thirdly, the heat generated by the electric current may harm the cells. Lastly, electrochemically generated toxic agents such as free radicals, gas and metal ions near the electrodes are harmful to the cells.
Variation of cellular properties, i.e., heterogeneity of cells during electroporation remains the biggest hurdle for achieving high-efficiency electroporations with low cellular toxicities. One known factor contributing to the heterogeneity is cell size. Larger cells tend to be easier to be electroporated. For a mixture of cells with different sizes, when larger cells are efficiently electroporated under certain voltage, the voltage is often not sufficient to electroporate smaller cells efficiently. At a field strength that smaller cells are efficiently electroporated, larger cells are usually irreversibly damaged because the voltage is usually too high for the larger cells to survive. Other factors, such as different cell membrane composition or cell maturity, may also contribute to the heterogeneity of cells.
Despite of numerous attempts to improve the efficiency of cell electroporations, the critical problem of cell heterogeneity remains unsolved. The efficiency, cell survivability and cost effectiveness of electroporation methods can be further improved. The disclosed devices and methods are directed at solving one or more problems set forth above and other problems.